ON MICROSCOPIC DISCOVERY. 



601 



tinder this order. The lichens grow on rocks, 

 the trunks of trees, old palings, &c., and are 

 more usually known by the names of wall- 

 moss and tree-moss. Their generic distinc- 

 tions are founded on a microscopic examina- 

 tion of their organs of fructification, which 

 commonly resemble little cups or shields. The 

 fuci (or sea-weeds) form a most interesting 

 class of microscopic objects ; there is a won- 

 derful variety of them, and the structure of 

 every genera is either exceedingly beautiful, 

 or singularly curious in its details. Plate 35, 

 fig. 38, exhibits a species of sea-weed, under 

 a superficial amplification of 100. The con- 

 fervas are aquatic vegetations consisting of 

 capillary tubes only, and in many of them 

 the mode of propagation is extremely simple : 

 in the conferva fontinalis, it consists merely in 

 " the enlargement of one end of the thread-like 

 plant into a globular ball, which afterwards 

 falls off and expands into a thread of the same 

 kind." The confervas include the genera 

 Chara, and Nitella, in which, as before ob- 

 served, the cellular circulation is distinctly 

 seen. The appearances presented under the 

 microscope, by the different kinds of mouldi- 

 ness is most remarkable. Every species is 

 resolved into a perfect plant, " bearing," says 

 Baker, " leaves, flowers, and seeds, and in- 

 creasing in a manner almost incredible : for 

 in a very few hours the seeds spring up, ar- 

 rive at full maturity, and bring forth seed 

 themselves; so that a day produces several 

 generations of them." The usual form of these 

 minute plants consist, of a capillary tube, the 

 stem, and a small round head, the fruit or seed 

 vessel ; this latter ripens, bursts open, and 

 scatters the seed around it. The fungi, of 

 which the common mushroom is a representa- 

 tive, " consists of plants mostly of a spongy or 

 cork- like texture ; they are generally of short 

 duration, and bear their seeds in gills or tubes, 

 or attached to fibrous or spongy substances. 

 Their generic characters are taken from the 

 disposition of their seeds, or from their external 

 figure or appearance. The greater number 

 of the fungi are indigestible poisonous matter, 

 and the edible mushrooms ought to be collected 

 with care." 1 Mr Pritchard observes, "their 

 structure is simple, and mostly consists of cell- 

 ular tissue, in which the minute seeds or 

 sporules are disposed. They are found in all 

 damp places in which there is not a free cur- 

 rent of air." Before the invention of the mi- 

 croscope, it was believed that the various kinds 

 of fungi " might be generated at any time, 

 and from any kind of putrified substance, either 

 animal or vegetable, without seed ; merely by 

 the friendly concurrence of either natural or 

 artificial heat and moisture." In reference to 



1 See Botanical Chart in the Popular Encyclopedia 

 VOL. li. 



this opinion, an old micrographer justly re- 

 marks : " It must be owned, that heat and 

 moisture, and oftentimes a degree of putrefac- 

 tion in the substance, are requisite to make 

 these little plants thrive ; but that such prin- 

 ciples should be able to create them, must, I 

 think, be past belief." The destructive fungi 

 of wood, (merulius destruens and vastator^) more 

 popularly known as the dry rot, are singular 

 microscopic objects when examined in detail ; 

 as are also the uredo segctum, &&. , which cause 

 rust, smut, &c.,in grain, and whose fructifica- 

 tion consists in a mealy powder, under the 

 cuticle of the plants. 



With a brief mention of the microscopic 

 phenomena exhibited in the woody formations 

 of trees, shrubs, &c., we shall conclude our 

 survey of the vegetable kingdom. " The stem 

 of trees and shrubs is covered externally with 

 a very fine cuticle, (rind,) under which lie 

 the bark and the liber (Bass,) the latter con- 

 sisting almost entirely of the most active sap 

 vessels, and consequently, one of the parts most 

 essential to the support of the plant. Placed 

 more internally, is the alburnum (sap ;) next 

 to it is the true wood, and next, the medulla 

 (pith) partly within the interstices of the wood, 

 partly down the middle of the stem; its quan- 

 tity gradually diminishing as the age of the 

 tree increases. In plants of this kind too, one, 

 or more properly, two new layers of wood are 

 produced yearly, probably by the alburnum, 

 whence it is possible, from the number of such 

 concentric layers, to form an estimate of the 

 probable age of the plant. The wood of palms 

 forms an exception to this disposition, in which 

 no such concentric layers exist, the trunk being 

 equally dense throughout, very hard, and ap- 

 parently traversed by partial tubes of albur- 

 num. This circumstance is of importance in 

 assisting the decision as to the nature of fossil 

 woods." In thin transverse and vertical sec- 

 tions of woods, (such as are prepared by Mr 

 Pritchard for the gratification of the micros- 

 copic observer,) all, or the greater part, of the 

 characteristics above named, are clearly dis- 

 tinguishable under a moderate magnifying 

 power. The great points of inquiry and ex- 

 amination in this class of objects, are the form 

 and disposition of the cellular tissue, woody fibre, 

 and vascular tissue. "The cellular tissue composes 

 the pith and soft parts of a tree or plant; when 

 minutely examined, it is found to consist of 

 distinct vesicles of various forms cohering 

 together: they vary in size from l-30th of an 

 inch to 1 -600th ; the largest are found in 

 aquatic plants and in the gourd tribe." This 

 cellular tissue, or the vesicles of which it is 

 composed, is filled with the nutritive juices 

 of the plant, whether absorbed by the bark or 

 furnished by capillary tubes from the root ; 

 and in these small reservoirs, it is probable, 

 4 a 



